1. Field of the Invention
The present invention relates to a method for manufacturing a capacitor. More specifically, the present invention relates to the following method for manufacturing a capacitor. A first protective layer, an element layer, which generates capacitance as a capacitor, and a second protective layer are deposited sequentially on a rotating supporting base. The first protective layer comprises resin layers. The element layer comprises resin layers alternating with metal thin film layers. The second protective layer comprises resin layers. At a point in the process of the deposition, the number of layers to be deposited further is determined, based on the deposition status up to that point, to provide a capacitor having a desired thickness of each layer, a desired entire thickness or a desired electrostatic capacitance.
2. Description of the Prior Art
A method for manufacturing a layered product having alternating resin layers and metal thin film layers, wherein depositing a resin layer and depositing a metal thin film layer are performed one after the other, and repeatedly applied to a rotating supporting base, is known, for example, from Publication of European Patent Application EP 0 808 667, which also discloses a compact capacitor with large capacitance by providing external electrodes in the thus obtained layered product.
Referring to the drawings, the following is an example of a method for manufacturing a layered product for a capacitor comprising resin layers and metal thin film layers.
FIG. 15 is a cross-sectional drawing schematically showing an example of a manufacturing apparatus using a conventional method for manufacturing a layered product for a capacitor.
An apparatus 900 for manufacturing a layered product includes a rotatable cylindrical can roller 910, an apparatus 920 for forming a resin layer, a resin curing device 940, and an apparatus 930 for forming a metal thin film, which are arranged near the perimeter of the can roller 910, inside a vacuum tank 901. The reduced pressure inside the vacuum tank 901 is sustained by a vacuum pump 902.
Liquid resin layer material is supplied to the apparatus 920 for forming a resin layer with a resin-material supply tube 921. The fluid flow can be regulated with a fluid-flow regulation valve 922. The fluid resin layer material is accumulated in a heating container 923, heated, evaporated, and deposited on the surface of a heating roll 925, which rotates in the direction indicated by arrow 924. Then, it is again evaporated, and deposited on the surface of the can roller 910, which rotates in the direction indicated by arrow 911.
Since the can roller 910 has been cooled below the condensation point of the resin layer material, the deposited resin layer material is cooled by the surface of the can roller 910, so that a solid resin layer made of the resin layer material is formed.
The resulting resin layer is cured by, for example irradiation of UV light from the resin curing device 940.
Then, the apparatus 930 for forming a metal thin film forms an aluminum thin film on the surface of the resin layer by vapor deposition. The metal thin film can be formed by using an oil margin method, where a strip of oil is deposited on the surface of the resin layer so as to prevent the formation of the meal thin film in the portion covered by the oil strip for a margin (insulating region). Thus, a striped metal thin film layer can be formed.
Thus, rotating the can roller 910, the apparatus 920 for forming a resin layer and the apparatus 930 for forming a metal thin film form resin layers alternating with metal thin film layers on the circumferential surface of the can roller 910, and a layered product comprising resin layers and metal thin film layers is manufactured.
The thus obtained layered product is cut and provided with external electrodes, whereby a capacitor as shown in FIG. 16 can be manufactured. The capacitor 950 shown in FIG. 16 includes a layered product comprising resin layers 951 and metal thin film layers 952 laminated alternately and a pair of external electrodes 954 formed on the opposing sides of the layered product. The external electrodes 954 are connected electrically to the metal thin film layers 952. The metal thin film layer 952 formed on each of the resin layer 951 is divided into two regions that are electrically insulated from each other by a striped margin 953 extending in the depth direction of the drawing. Therefore, different electric potentials are supplied to the pair of external electrodes 954, so that the capacitor 950 can function as a capacitor having the resin layers 951 as a dielectric layer.
Considerable R&D efforts have been invested in this method, since with this method, a resin layer thickness of about 0.05-1 .mu.m, and a metal thin film layer thickness of about 20-100 nm can be attained. A more compact capacitor with larger capacitance can be manufactured with lower production costs, compared with a conventional capacitor obtained by laminating metallized films obtained by forming a metal thin film layer on a polymer film by vapor deposition.
With acute technological development competitions, uniform components with high quality are in demand increasingly. This applies to the field of capacitors, and there is a need for compact capacitors with large capacitance and uniform and constant quality.
Under these circumstances, the above-described method hardly can achieve intended thicknesses of resin layers and metal thin film layers and an intended width of margins stably. The thicknesses of these layers and the width of margins can vary with various factors. The thickness of the layers can be affected, for example, by the amount of resin layer material or metal material evaporated. Especially, since the resin layer material is polymeric, it is much more difficult to maintain the amount of the resin material evaporated constant all the time than to control the amount of the metal material evaporated. Further, the width of the margin can be affected by the width of the patterning material (oil) applied to the surface of the resin layer or the amount of the material applied.
The thickness of the resin layer affects the capacitance and the total thickness of a capacitor to be obtained. The thickness of the metal thin film affects the total thickness of a capacitor to be obtained. Therefore, without controlling the thickness of each of the layers sufficiently, the capacitance and the total thickness of the obtained capacitor would be significantly outside of a targeted value, and the dispersion thereof would be outside of an intended acceptable range.
Further, the width of the margin is correlated closely to the area where the metal thin film layers for functioning as electrodes of the capacitor are formed. Therefore, without controlling the width of the margin sufficiently, the capacitance of the obtained capacitor would be significantly outside of a targeted value, and the dispersion thereof would be outside of an intended acceptable range.
The deviation from the targeted value of the electrostatic capacitance of the obtained capacitor or the dispersion thereof influences the performance of a product having the capacitor incorporated therein significantly. Moreover, the deviation from the targeted value of the outer size (thickness) of the obtained capacitor or the dispersion thereof is a detriment to the mounting onto a circuit substrate or the like.
Furthermore, unexpected variations in the thickness of deposited layers or the width of margins occurring in the process of the deposition may not be detected, or even if they can be detected, it may not be possible to accommodate the variations sufficiently in the subsequent processes in the deposition of the layers. In this case, the whole layered product formed on the can roller 910 becomes a defect, thus resulting in a large loss.
Furthermore, a protective layer comprising resin layers and/or a reinforcement layer comprising metal thin film layers and resin layers laminated alternately may be formed on at least one side of an element layer, if necessary. These layers are formed in order to protect the element layer, improve the adhesion strength of the external electrodes or the like. The thickness of the protective layer and/or the reinforcement layer makes up 10 to 20% of the whole thickness of the capacitor, which is large. Therefore, without controlling the resin layer and the metal thin film layers in these layers sufficiently, the functions as the protective layer or the reinforcement layer cannot be fulfilled sufficiently. In addition, the total thickness of the obtained capacitor would be significantly outside of a targeted value, and the dispersion thereof would be outside of an intended acceptable range.